1. Field of the Invention
The present invention relates generally to the field of aircraft collision avoidance procedures and, more particularly, to procedures for establishing aircraft en route conflict alerts.
2. Description of Related Art
Each airborne aircraft has surrounding it an imaginary safety or nonintrusion zone. These safety zones are such that when one aircraft intrudes into the safety zone of another aircraft, a mid-air collision may be possible. Within the United States, the Federal Aviation Administration (FAA) establishes the extent of aircraft safety zones and currently provides for disc-shaped safety zones which, under specified conditions, are 10 miles in diameter and 2,000 feet in height. Similar aircraft safety zones are, in general, established in other countries of the world by national FAA counterparts.
Air route traffic control centers (ARTCC's) are, as is well known, maintained throughout the world. It is a principal responsibility of air traffic controllers operating these ARTCC's to monitor and direct en route air traffic in such a manner that air safety is assured. As part of their responsibility for assuring air safety, air traffic controllers continually attempt to maintain sufficient separation among aircraft under their control that no aircraft's safety zone is violated by another aircraft.
Typically, aircraft positional data required by air traffic controllers is provided by ground-based radar associated with the ARTCC's and the aircraft-carried transponders. Such transponders provide aircraft identification and aircraft altitude data determined by on-board altitude measuring equipment. Data output from the radars and transponders is processed by computer portions of the ARTCC's and aircraft status is displayed on a CRT screen for use by the air traffic controllers.
The air traffic control computers are also typically programmed to provide information as to actual and impending aircraft safety zone intrusion. In response to the detection of actual or near-future (usually 1-2 minutes) safety zone intrusions the computers cause aircraft en route conflict alerts to be displayed on the air traffic controllers' monitoring screens. Such conflict alert displays typically also provide identification of the aircraft involved and the controlling sector or sectors. In response to the conflict alerts, the responsible air traffic controller or controllers give appropriate altitude and heading directions to the involved aircraft to eliminate or prevent the intrusion and cancel the conflict alert. Current FAA practices relating to en route aircraft conflict alerts are, for example, detailed in a technical report entitled "Computer Program Functional Specifications for En Route Conflict Alert," Report No. MTR-7061, dated October, 1975 and published by The Mitre Corporation.
The accurate determination or prediction of conflict alerts, of course, requires a precise knowledge of position and altitude of all aircraft within the traffic control system sector. Moreover, to accurately predict near-future conflicts, precise information as to aircraft velocity vectors are also required. Ground-based radar is not, however, usually capable of determining aircraft altitude with sufficient precision to provide accurate conflict alert determinations and predictions. Reliance as to precise altitude is, as a result, placed upon information relayed from the aircraft via their transponders. The accuracy of the aircraft generated altitude information is, in turn, dependent upon such factors as the continual updating, within the responsible ARTCC, of local barometric pressures along the aircraft's flight path.
As a result of imprecise determinations of aircraft position, and especially of aircraft altitude, present procedures for determining and predicting en route conflict alerts tend to cause excessive false alarm alerts. In addition, many actual or impending conflicts may not be detected and hence cannot be displayed as conflict alerts. Of significant concern to the FAA and other international air traffic control organizations is the effect false alerts have on air traffic controller productivity and, as well, the effect they have upon air safety. If the processes used frequently fail to detect conflict alerts with sufficient warning time so that the controllers and pilots can maneouver the aircraft and avoid actual conflicts, then the processes are only marginally effective and their usefulness as aids to the controller is questionable. Conversely, since each and every conflict alert demands the attention of the responsible controller to examine the situation and determine the action appropriate for the situation, if a significant number of conflict alerts are generated which turn out to be false alarms (that is, no action is taken by the controllers or pilots and an actual alert never occurs), the believability of the process is reduced. Moreover, the time required on the part of the controllers to react to each alert may actually reduce the controller's effectiveness in maintaining safe air traffic flow.
The solution to the problem of frequent false alarm conflict alerts and occassional missed detections is not to ignore conflict alerts but, instead, to improve the accuracy of determining conflict alerts so that they can by fully relied upon by the air traffic controllers.